1. Field of the Invention
The invention relates to a back rest for vehicle seats, particularly motor vehicle seats.
2. Description of the Prior Art
In the known back rests of this type, the yoke portion, like the side beams, consists of steel sheet and is welded to the side beams. The rigid connection produced thereby between the ends of the yoke portion and the upper ends of the two side beams has the result that, in a flexing of the yoke portion as a result of a strong load acting in the longitudinal direction of the seat, the side beams experience a twisting distortion, which can substantially reduce their load-carrying capacity in the pivot direction of the back rest.
Since such a decrease in the load-carrying capacity of the side beams must be avoided as far as possible for safety reasons, it has already been proposed to replace the yoke portion with a spring steel band which wraps around the side beams from behind and is attached only on the outside thereof. In such a construction, under a heavy load from the front of the back rest, as can occur, for example, in an accident, the side beams are only subjected to a bending load, and not a torsional load. It is, therefore, sufficient to make the side beams adequately stiff to handle the occurring bending loads. This arrangement is possible and results in a significantly lower expense, lower weight and less required space in comparison to such side beams which experience a torsion and must also have their full load-carrying capacity even in their twisted condition. This advantage is accompanied by a disadvantage, however, which leads to problems, especially when the seat is built into a vehicle in which relatively little room is available in the longitudinal direction of the seat. Under a load on the back rest from the front, the spring steel band can bend so far backward, under given conditions, that a person located behind this back rest can be endangered or even injured thereby. If the support bars of a head rest are attached to the spring steel band, then during a bending out of the band, these support bars or their mounts in the head rest can be deformed. A further disadvantage is that the side beams draw closer together during a bending of the spring steel band, which can result in a lateral pressure being exerted on the seat user.